Especially abilities that mean more power - the power to make rainbows is one thing, but mindreading is quite another. For many people, anyway.
There are scans that can be conducted to look for genetic mutations of other kinds - I can simply tweak these tests to pick up the x-gene, we would just need a DNA sample. Would you be alright with a cheek swab?
Oh, and I'm Hank McCoy, by the way! Scientist with the Department of the Navy.